The present invention relates generally to devices, systems and methods for the testing of gas detectors, and especially, to devices, systems and methods for calibrating or testing a response of one or more gas sensors of one or more gas detectors to one or more analyte test gases.
Gas detectors including one or more gas sensors (for example, electrochemical gas sensors, combustible gas sensors, etc.) are well known for monitoring for potentially hazardous gases in various environments. Generally, gas from the environment to be monitored comes into contact with the sensors(s) within the detector by diffusion or by forced flow. Electronics within the detector convert the output signal from the sensor(s) into one or more signals representative of a gas concentration. The sensor output per unit amount of gas can vary with time and hence periodic calibration is required to ensure that the detector reading is accurate.
Currently, sensors of gas detectors are calibrated by passing a calibration gas having known, fixed compositions of one or more analyte gases from a compressed gas cylinder into the detector, thereby displacing ambient air within the detector and exposing the sensor(s) to the calibration gas. The calibration gas is allowed to flow until the sensor output reaches a steady state. Since the calibration gas has a known composition, the output signal from each sensor of the gas detector can be adjusted to provide an accurate measure of analyte gas concentration. Excess calibration gas flows out of the detector. In the interval between full calibrations, an intermediate test (sometimes referred to as a bump test) can be performed to ensure that a sensor or instrument is responding to a specific analyte test gas. As used herein, the term “testing” refers generally to all types of analysis of the operation of a gas detector and includes, for example, full calibration and bump testing.
Safe commercial practice dictates that sensors within a gas detector be tested, including calibrated, at a minimum according to the manufacturer's recommendations. Various calibration/testing systems and methods have been developed to facilitate gas detector testing. Gas detector calibration/testing systems are disclosed, for example, in U.S. Pat. Nos. 5,239,492, 4,854,153 and 5,655,894. European patent No. EP 1 342 082 discloses a calibration system for use with a portable gas detector.
Moreover, several calibration/testing systems are commercially available in the United States. For example, the MICRODOCK™ automatic test and calibration station available from BW Technologies of Canada provides a calibration and bump testing station for the GasAlertMicro™ multi-gas detector. One inlet is provided for ambient air, and another inlet is provided for connection to a single pressurized gas cylinder. As described in the MicroDock Automating Test and Calibration Station User Manual (2103) available from BW Technologies, multiple gas detector docking modules can be connected to the system. However, test gas can flow to only one connected docking module at a time and thus only one gas detector can be calibrated at any one time. Also, the TIM® Total Instrument Manager calibration/testing system is available from Mine Safety Appliances Company of Pittsburgh, Pa., which provides, among other functions, full calibration and bump testing for several Mine Safety Appliances Company gas detectors, including multi-gas instruments and single gas monitors.
Although strides have been made in facilitating testing of gas detectors, a number of problems still persist. Among other problems, currently available calibration systems can require time consuming changes in connections of gas cylinders and gas detectors as well as changes in test conditions to test a single or multiple gas detectors with one or more test gases.
It thus remains desirable to develop improved (for example, more automated) devices, systems and methods for testing of gas detectors.